To tell you the truth, this is one of those types of questions that everyone initially thinks is obvious, but given some thought, it is realized that this problem is more complex than initially thought.
I don't have the exact answer for the question but what I do know is that throughout the books I was reading, I have yet to come across a sheikh saying that you have to know the reward in order to get the reward. And Allah (swt) is more merciful and just than to make you know the rewards of every act you do in order to get the reward.
I hope I make sense insha allah.
This ayah came to my mind when I read this thread :
" إِنَّهُ مَنْ يَتَّقِ وَيَصْبِرْ فَإِنَّ اللَّهَ لَا يُضِيعُ أَجْرَ الْمُحْسِنِين" "Indeed, he who fears Allah and is patient, then indeed, Allah does not allow to be lost the reward of those who do good" (surah Yusuf: 90)
I agree with brother muslim56. I have also never heard a sheikh saying you must know what the reward is. No doubt it is best to know what the reward is, for that may motivate a person to be persistent in doing the good deed, but I doubt that it's a requirement, Wallahu A3lam.
It doesn't matter as long as the reason you did that good deed, was for Allah. It's not our good deeds that will get us to Paradise, it's Allah's mercy. Never have i ever heard that you have to know the reward of a good deed before doing it